Production of titanium pigments



' i from suclr'priorprocedures especially notab Patented Apr. 4, 1944 ritonuc rrou or TITANIUM PIGMENTS I John Lewis'Keats, Wilmington, DeL, assignor to E.-I. du Pont de Nemcurs & Company, Wil- .mington, Del.,a corporation of Delaware No "Drawing;

invention' relates-to the preparation of pigment-quality titanium compounds and-more particularlyjto the productiono! titanium oxide useful for pigment purposes, More'speciflca1ly. it I relates to novel methods for producing such pig- Application September 22, 1939, SerlalNo.296,069-

- tures and at the pressures corresponding to such I elevated temperatures; and finally, that the hydrolysis precipitate from such procedure is, upon mere drying, and without recourse to calcination menttitanium oxide through hydrolysis titaniferous solutions while maintaining the sameunder superatmospheric temperatures and pressurea V In a more restricted-sense, the invention reto develop pigmentary properties, adapted for direct'use as a pigment; I

In accordance with this invention, therefore,

'uncalcined, pigment-grade titanium compounds.

I and particularly anhydrous titanium oxide, are

r lates to a novel method, for'producingpigmentaiy titanium oxide by hydrolyzing titanium saltsolutions under such conditions'ofitemperafi lre and pressure that the precipitate obtainedfromsuch hydrolysis comprises a substance having fully developed pigment ,properties and which requires" no calcinaticn treatment to, developessential'and required pigment characteristics.

Various attempts have'been made previously (e. g., U. S. Patents 13402256, 1,489,417, 2,118,916) to procure uncalcined'titanlumoxide whichwill possess satisfactory pigment characteristics. 7 All such prior efforts, however, have tailed to attain their object. 'Ineach instance the hydrolysis precipitate whichis recovered must be subjected to calcination treatment and'at, relatively high temperatures in order to develop therein such essential iement characteristics as desired-par ticlecolor; ioilgh scmtic opacityltmtine .In a more specific and preferred embodiment, pigment quality,- uncalcined, anhydrous titanium obtained by'subjecting'titaniferous aqueous solutions-to hydrolysis under superatmcspheric pressures and'controlled, critical, elevated tem perature conditions "of the order of at least oxiderexhibiting excellent, fully developed tinting strength and other essential pigment characteristics, is obtained by-subjecting an aqueous titanium. saitsolutiony particularly Ja sulfate or chloride, to hydrolysis at temperatures ranging I from substantially 350 C. to about 450 C. and at -superatrnospheric. pressures corresponding to such'temperaturesfi gIn carryingeout-Ithe invention, after preparing a titanium salt-solution such as the chloride, sulannouncenputs; oxalate, etc, for hydrolysis strength; etc; j Thei ltlntingstrength oi products poor. and, unless :subiected? to calcination,

products are incapable or se as ime pigments} the? objects of this invention to". 1 i overcome these ismdfother' disadvantages which Itis among preparing a superior type of titanium oxide pig-' ment Possessing .fullydeveloped hiding power and cther-essential-pigment properties without bein subjected to calcination treatment. j"A further a are aflordedby products irom prior processes, and to provide in particular; a novelmethod for:

accordance with wcll-lmown procedures, said v." solution is introduced into {closed reaction zone orchaniber." as, asuitahle autoclave or bomb tm oi vcsseli; adapteditciwithstand relatively hightcmperatures and -superatmospheric pressures; Y Thezjsoluticn is then hydrolyzed within such cicscd ccutainer, such-hydrolysis being efiectedat a temperature-;.or atleast 225 C. and under the pressuregencrated'by the solution at.

such'temperaturep or,-,if -;desired, at higher pressures. Preterablm-and'toobtain a product which exhibits satisfactory, optimum pigment properties, especially improved tinting strength, said hydrolysis is conducted atftemperatures ranging object is to provide a novel processjoa y m t 1 superior titaniumoxide pigments without resort ing to calcination of such precipitate and through themedium of hydrolyzing titanium salt solutions at elevated temperatures andlpressures.

" tures.

These and other objects are attainable in this invention which embodies the discovery that the physical characteristics oi hydrolyzed titanium compounds are greatly influenced by the conditions' which prevail during hydrolysis; that, furthermore, improved, pigment-useful titanium ,compounds, particularly anhydrous titanium oxide, may .be readily obtained by conducting such hydrolysis at certain elevated, critical temperau from substantial-1y 3501C, to about 450 C. and under pressures jcorresponding to such tempera- The time of 'treatment which is required to ellect substantially complete hydrolysis of the solution will vary and will depend upon the temperatures and pressures used, as well as the relative concentration of the solution being treated. Usually, such time period ranges from about 1 to 3 hours. Upon completion of hydrolysis, the hydrolysis precipitate is suitably recovered, which, upon being suitably washed and then dried at a temperature of approximately C., will comprise a novel anhydrous product (not a basic sulfate), of fully developed pigment properties and which require no calcination held at that temperature for one hour. The pretreatment to develop such properties. cipitate was washed and dried. It was charac- To a more complete understanding. of the interized in the uncaicined state by tinting strength vention, the following examples are' given, each in the same range as pigments prepared by calbeing in illustration but not in limitation of the 5 cination procedures.

invention: Example IV Ewample I I Twent -tw cc. of anh drous TiCl was di- A solution of tittmyt sulfate of the touowmg luted with Welter to give solution (:ontaining composttmnt G 27.5 grams T102 per liter and 50 grams HCl per m 52 liter. This solution was heated to 360 in the per 1 i r 466 autoclave used in previous examples and held at g g z fi' l g g- -gg g-gf gg;""- 0 ()7 360 for one hour. The solution was completely Cr per liter (in the form of sulfate) 0.02 hydmtyzed ttt the end the heatmg pemd' The precipitate was washed and dried. It was was prepared by dissolving TiOSO4.2H2O which examined by the powder X-ray method to de-" was crystallized from an impure titanium sulfate termine the crystalline odificati n and was solution such as is obtained by attacking ilmenite shown to be rutile. The lines in the X-ray difwith H2804. A volume of the above purified fraction pattern were very'sharp like the lines titanyl sulfate solution was placed in a. tantalum' 2 n the p t s of calcined P e se e tube and the tube placed in a closed bomb. The dried product was also characterized by tinting bomb was heated by means of an induction furstrength in the same range as the best rutile nace to a temperature of 400 c. and held at p m ts pr p ed y th c in tion pr e ure. that temperature for a period of one-hour. When Although the invention has been illustratively the tube was removed from the bomb after heatdescribed in the foregoing exampl s as ap ing, it was found that the solution had completely ble to the hydrolysis o tanium sulfate and hydrolyzed, The precipitate was washed to retitanium chloride solutions, the same is not to move H2804 and traces of Fe and Cr originally be considered as limited to such illustrated appresent; i th liquor nd a dri d t; 100 plications. Other titanium salt solutions may be The dried product was found to consist of an subjected to hydrolysis in accordance with the hydrous 10 th t any omb water or invention, examples of such othersalt solutions H2804 such as is present in the dried products of titanium including e nit ate, oxalate or from hydrolysis at lower temperatures. The fluoride. dried, uncalcined product was tested for tinting Also, though the invention comprises heating strength and color and was found to be superior an aqueous solution of a titanium salt in closed in regard to these .properties. The tinting vessels at critical temperatures ranging from at strength was equal to that of the best anatase oble st 225 C. to substantially 450 C., and preftained by calcination procedures. erably within the range of 350 C. to 450 C.,

Example H under pressures corresponding to the tempera- 40 ture of the solution under treatment, it is to be Titanium sulfate solution (350 cc.) obtained by d r t t at any higher pressure may be used, attacking ilmenite with H2804 a d i g t e if desired, and without disadvantage so far as following composition: the process of this invention is concerned, pro- Grs-ms vided only that the pressure imposed is within T103 per liter 2 the safe limit for the equipment employed. In Fe per liter 36 any given instance, the minimum pressure re- Total H2804 per lite 600 qulred will depend upon the temperature and, was diluted with water to give a concentration of composition 9 the solution I 140 grams T102 per liter, and the diluted solution As already indicated Observance of certain placed in the tantalum tube as in Example I and 50 critical temperatures must be in der o heated at 360 for a period of three hours. The procure a Product which possesses is e tintsolution was completely hydrolyzed by this treat ing strength values to afford its direct use as a m; giving a yield of approximately 100% of pigment without any calcination treatment. the theory. The precipitate after removal from should temperatures below for the pressure tube was washed and dried at 100. 5 stance. of the de 200 be The dried product was characterized by tinting used.development of e plete p en strength equal to that of products prepared by strength will be mum! lacking, h e t e conventional calcination procedures. g l l g o igeti) being deficient in this Essen" g a a one, w e useless for employment in. Exttmpte commercial pigment applications. On the other The double salt, sodium titanium sulfate was hand, when resort is bad to temperatures of the prepared by adding sodium chloride crystals to order of at least 225 0., and especially within a. solution of titanium sulfate and heating the the range of 350 to 450 0., the recovered mixture as specified in U. S. 1,357,690. The hydrolysis product will comprise a substantially double salt was washed to remove iron and the completely developed pigment substance of relcrystals dissolved in dilute H2504 to give a soluatively fine, uniform particle size, of dense, soft tion of the following composition: texture, and having tinting strength, color and y Grams oi1 absorption values substantially approximate E22 $r 3?; to those exhibited by present commercial, calpe1' er cined titanium oxide i ments. In such Fe per liter (in the form of sulfate) 0.01 p g conch tion, the product will be eminently adapted for per liter (tn the form of I direct use as a pigment in all manners of appli- The resulting solution was heated in a pressure cation. tube or autoclave to a temperature'of 360 and In d pting the invention. it will also be found calcium or barium sulfate,

that a product having requisite tinting strength a and color is more effectually obtained when certain optimum ranges of acid concentration are employed during the pressure hydrolysis. Thus,

when hydrolyzing titanium sulfate solutions at a temperature of, say, 360 0., a concentration ranging from about 3.1 to about 5.5 gram-mols H2804 per liter of solution will be most preferable for use; whereas, when .hydrolyzing-titanium chlo'-' ing from substantially 2.0.to 6.0 gram-mols of H2804 per liter are efiectively useful; while acid concentrations ranging" from 0.5- to 5.5 grammols of HCl per liter of solution are desirable for use when hydrolyzing 'titanium chloride solutions. r f

Although use is preferred of an perature limit of substantially450? 0., temperatures of a relatively higher order and up to sub-- stantially 550 C. may also be used, with a corresponding correlated pressure condition. In such instances, however, some loss in brightness may result, unless avoided by suitable adjustment of the time of treatment. Likewise, though the invention has been illustrated in connection with the precipitation and recovery of titanium oxide products per se, complex or extended types of pigments may be suitably obtained by eifecting hydrolysis in the presence of various base materials or extenders such as various alkaline earth metal sulfates, particularly or silicates; or the process may be conducted in such manner that co-precipitaticn of the T102 pigment and extender or base material may be had, such as by efiecting hydrolysis in the presence of soluble compounds adapted to yield tion the extender or base materials mentioned.

As will be apparent, the invention affords the direct obtainment from the hydrolysis process of a product having' fully developed pigment properties, which product prior to use need only be subjected to conventional washing and drying to remove water. As a consequence, there is desirably avoided the previously required calcination step to develop pigment properties. This is very advantageous, not only because of the fuel savings which thereby result, but there is eliminated the danger of sintering of pigment particles during calcination,,whereby production of a more uniform particle size pigment is assured. Previously, sary to the development of commercially satisfactory pigment strengths to calcine the raw pigment at temperatures ranging from substantially 800 to 1050'C. At such temperatures, undesirable sintering of the particles usually occurs, so that the product obtained as a result of such calcination is relatively coarse and gritty and must therefore be subjected to prolonged grinding in an attempt to reduce to some extent the sintered aggregates. As noted, the instant invention afiords the elimination of this objectionable calcination step and the direct production of a fully developed pigment product from the hydrolysis, which product is inherently soft and smooth in texture and free from sintered aggregates or other injurious efiects arising by reason of high calcination temperatures.

through precipitaupper teintion are that the products from the hydrolysis are easilyfllterable, whereas the products from 1 hydrolysis of titanium 'saltjsolutions,

larly titanium chlorideiat atmospheric are often to filter.

I claim as my invention:

1. A process "for anhydrous titanium tially fully-developed pigment properties including tinting strength, comprising subjecting an aqueous relatively pure solution of ahydrolyzable pressure,

titanium salt solution having an acid concentra the same at a temperature ranging fromv 350 to 450 C. and under the pressure generated. by

product.

2. A process for producing an uncalcined, anhydrous titanium oxide product of substantially fully-developed pigment properties, including substantially fully-developed pigment properties, and then purifying and recovering the resulting pigment grade product.

3. A process for producing an uncalcined anhydrous titanium oxide product of substantially developed, anhydrous titanium oxide pigment directly from hydrolysis and without any calcinaa substantial yield of anhydrous crystalline TiOz with substantially fully-developed pigment properties and thereafter recovering, washing and Additional advantages afforded by theinven Darticul colloidal in natureland very difficult producing an. oxide product of.- substan- 

